Add support for releases

[aexvir]

We should display the project releases within The Zoo itself, it should be fairly simple if we don't want to store them in our DB, but in the future, when we'll have a more reliable service-to-service dependency graph it would be nice to notify the dependant services when there is a new release on the dependency.

On the service details view, we already show some handy info about the service itself. We could extend that view to also include information about releases and their changelog from platforms like GitLab or GitHub. We'll just have a new tab on the service details menu, and a new API view that would fetch the releases data from our own database.

In order to have the releases in our database we'll just have a periodic celery task that will save the releases to our system. We'll just store the version, release name, changelog and links to artifacts.